Dynamic gas bearing of a motor spindle comprising aeration

ABSTRACT

The invention relates to a dynamic gas mounting of a motor spindle, with a rotating shaft  2  which is gas-mounted in a housing  3  in the radial and axial direction, at least one radial gas bearing  4  being present for radial mounting along the shaft  2  and at least two axial gas bearings  5, 6  being present for the axial mounting of the shaft  2 , and the two axial gas bearings  5, 6  having different surface profiles  12  for generating a flow of the bearing gas in the axial direction  14  of the shaft  2  in order to vent the mounting.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. §119 of German Application No.100 37 077.2 filed Jul. 27, 2000. Applicant also claims priority under35 U.S.C. §365 PCT/DE01/02677 filed Jul. 23, 2001. The internationalapplication under PCT article 21(2) was not published in English.

The invention relates to a dynamic gas mounting of a motor spindle,having the features of the preamble of patent claim 1.

The known prior art includes dynamic gas mountings of motor spindles, inwhich the air gaps of the radial and axial gas bearings are reduced, atleast in regions, over an increasing operating time, particularly onaccount of abrasion and soiling. As a result, the starting resistance ofthe dynamic gas mounting is increased and synchronous stability isreduced.

The object on which the invention is based is to offer a dynamic gasmounting of a motor spindle, in which there is no undesirable variationin the running properties of the gas mounting.

This object is achieved by means of the features of the characterizingpart of patent claim 1 in conjunction with the features of the preamble.Advantageous embodiments of the invention are described in subclaims2-15.

In the gas mounting according to the invention, the at least two axialgas bearings possess different surface profiles for generating a flow ofthe bearing gas in the axial direction of the shaft in order to vent themounting. A bearing gas flow is consequently generated within thehousing of the gas mounting and in the air gap of the radial and axialbearings, with the result that undesirable foreign particles (forexample, dirt particles or abrasion) are removed and the mounting isvented and cleaned. Thus, an undesirable variation in the air gap of thegas mounting is avoided and the gas mounting can be operated with a longuseful life and high running accuracy, largely maintenance-free, byvirtue of continuous gas scavenging as a result of the continuouscleaning which occurs. By “surface profile” is to be meant a surfaceconfiguration with elevations/depressions formed in regions, and thesemay also be generated by means of corresponding coatings. So that thebearing gas, in particular the bearing air, can be sucked in andexpelled, the housing of the gas mounting possesses at least twoorifices for the introduction and discharge of the flow of bearing gas.Advantageously, at least one orifice is provided with a filter element,in order to avoid soiled ambient air being sucked in.

The dynamic gas mounting according to the invention refers, inparticular, to a fast-rotating motor spindle, that is to say a motorspindle in the rotational speed range from about 10,000 revolutions/minto about 200,000 revolutions/min. By “dynamic gas mounting” is to bemeant, in contrast to static gas mounting, a self supporting gasmounting without the external supply of bearing gas, in particular ofcompressed air.

In an advantageous embodiment, the axial gas bearings are designed asspiral-flute axial bearings which carry different spiral-flute profilesas surface profiles. The different spiral-flute profiles produce apressure difference between the two axial gas bearings when the motorspindle is starting and rotating, so that the desired flow of bearinggas in the axial direction of the shaft is generated. For this purpose,bearing air is sucked in via an inlet orifice of the housing and flowsthrough the housing and, in particular, the air gap of the radial andaxial gas bearings, in order thereupon to leave the housing againtogether with the picked-up foreign particles. Consequently, theinterior of the housing and, in particular, the air gap of the gasbearings are kept dirt-free as a result of the cleaning and of thebearing gas flow.

In a particularly advantageous embodiment, the two axial gas bearingsmay be formed by a shaft shoulder of the shaft, one side of the shaftshoulder forming the first gas bearing and the other side of the shaftshoulder forming the second gas bearing. In this case, a shaft shoulderof this type is provided on one side with a first surface having a firstsurface profile and on the other side (rear side) with a second surfacehaving a second surface profile. According to the invention, in thiscase, different surface profiles, that is to say different in terms oftheir position and/or design, are provided, with the result that, duringthe operation of the motor spindle, a pressure difference arises betweenthe two surfaces and consequently between the axial gas bearings and thedesired bearing gas flow is generated.

According to a further advantageous embodiment, first and second surfaceprofiles formed in annular regions are provided in each case on thefirst and the second surface of the at least one shaft shoulder. Theannular regions may in this case be interrupted or continuous and bearranged on the various surfaces at a different distance from the centerpoint of the shaft. In the case of annular regions arranged between aninner radius r_(i) and an outer radius r_(a) of the shaft shoulder, theannular regions may have different outer radii r_(a) and/or differentinner radii r_(i). The surface profiles arranged in the annular regionsthereby acquire a different arrangement, as a result of which, duringthe interaction of different surface profiles, the desired pressuredifference for generating a flow of the bearing gas is induced.

The surface profiles may be designed, for example, as a stepped profile,a partially inward-shaped profile, a partially outward-shaped profile ora herringbone profile. This is explained in more detail in connectionwith the drawing figures.

The invention is explained in more detail by means of exemplaryembodiments in the drawing figures of which:

FIG. 1 shows a sectional view of a motor spindle with the gas mountingaccording to the invention,

FIG. 2 shows an illustration of a surface profile of an axial gasmounting as a stepped profile,

FIG. 3 shows a basic illustration of a shaft shoulder of the shaft withan annular region for forming a surface profile,

FIG. 4 shows an illustration of a surface profile of an axial gasbearing as spiral-flute profile,

FIG. 5 shows an illustration of a surface profile of an axial gasbearing as a partially inward-shaped profile,

FIG. 6 shows an illustration of a surface profile of an axial gasbearing as a partially outward-shaped profile, and

FIG. 7 shows the same as a herringbone profile.

FIG. 1 shows a longitudinal section through the housing 3 of a motorspindle with a motor space 27 having a motor 1, for example anelectronically commutated DC-motor, for driving the shaft 2, at whoseend facing away from the motor 1 is mounted an optical element, forexample a mirror element 7 or a polygonal mirror.

The invention relates, in particular, to the dynamic gas mounting of afast-rotating scanner motor spindle (scanner motor) for digital imageprojection, for example for the exposure of film-sensitive materials orfor projecting an image onto a viewing screen.

The shaft 2 is mounted in the housing 3 in a radial gas bearing 4 and ina first axial gas bearing 5 and a second axial gas bearing 6. The axialmounting is formed by the shaft shoulder 11 of the shaft 2, a firstsurface 15 having a first surface profile 12 being located on one sideof the shaft shoulder 11 and a second surface 16 having a furthersurface profile 12 being located on the other side (rear side) of theshaft shoulder 11. By a different selection and/or arrangement of thesurface profiles 12 on the first and second surfaces 15, 16 of the shaftshoulder 11, when the shaft 2 is in operation a pressure differencearises between the front and the rear side of the shaft shoulder 11,that is to say the first axial gas bearing 5 and the second axial gasbearing 6, with the result that the desired flow of bearing gas in theaxial direction 14 of the shaft 2 is generated.

This flow of bearing gas, in particular of bearing air, flushes throughthe air gap 13 between the shaft 2 and the radial gas bearing 4 andthrough the air gap 19 on the front and the rear side of the shaftshoulder 11. As a result, the bearing air is sucked in through theorifice 8 having a filter element 10 and a seal 28 and is dischargedthrough the orifice 9 which is designed as a gap 21 between the frontcover 20 of the housing 3 and the shaft 2. In this case, for example,disturbing and/or foreign particles present between the radial gasbearing 4 and the shaft 2 are picked up and, after flushing around theshaft shoulder 11, leave the housing 3 of the mounting through the gap21, during which time, in particular, heavier disturbing and/or foreignparticles may also be deposited in the cavity 29.

In the present case, the orifice 8 serves as an inlet orifice for theambient air and the gap 21 as an outlet orifice for the generated airflow. Depending on the operating state of the motor spindle, a reversedirection of flow may also occur, for example, during run-up or braking.In this respect, an air flow may also occur from the gap 21 to theorifice 8. The gap 21 may in this case also be provided with a filterelement (not shown).

Furthermore, particularly when a mirror element 7 is mounted at the endof the shaft 2, an end housing cover of the housing 3 may also beprovided in order to encase the mirror element 7. In a casing of thistype, an orifice (with a filter element) may also be formed (not shown)for the introduction/discharge of the bearing gas flow. Alternatively, adefined orifice may be provided (likewise not shown) in the cover 20 ofthe housing 3.

Various possible arrangements of the surface profiles 12, for example onthe shaft shoulder 11 of the shaft 2, are explained in the followingFIG. 2-7.

FIG. 2 shows an axial gas bearing which has a stepped profile as asurface profile 12, the individual steps 22, 22′, 22″ being shown by wayof example as continuously illustrated steps 22 and being arranged indifferent planes to one another (for example, rising/falling or wavy).

FIG. 3 shows a basic illustration of an annular region 17 with an innerradius r_(i) and with an outer radius r_(a) on a surface 15, 16 of ashaft shoulder 11 of a shaft 2 with a center point 18.

FIG. 4 shows, by way of example, a spiral-flute profile 23 as thesurface profile 12 between the inner radius r_(i) and the outer radiusr_(a) in the annular region 17 which is obtained.

FIG. 5 shows as a surface profile 12 a partially inward-shaped profile24 which may be arranged continuously or in an interrupted manner in theannular region 17.

FIG. 6 shows a partially outward-shaped profile 25 as the surfaceprofile 12 in an annular region 17 shifted inward with respect to FIG.5.

In a particularly advantageous embodiment of the gas mounting accordingto the invention, one surface 15 possesses a surface profile 12 in anouter annular region 17 (for example, a profile according to FIG. 5) andthe second surface 16 possesses a surface profile 12 in an inner annularregion 17 (for example, a profile according to FIG. 6). In this case,the inner radius r_(i) of the outer annular region 17 may reach orexceed the outer radius r_(a) of the inner annular region 17.

FIG. 7 shows, as a surface profile 12, a herringbone profile 26 which isarranged in a sector region or continuously.

By the illustrated or further surface profiles 12 being combined on thesurfaces 15, 16 of the shaft shoulder 11 of the shaft 2 of the motorspindle, the sought-after pressure differences between the surfaces 15,16 can be generated, and consequently the desired bearing gas flow inthe axial direction 14 of the shaft 2 can be brought about.

1. A dynamic gas mounting of a motor spindle, with a rotating shaftwhich is gas-mounted in a housing in the radial and the axial direction,at least one radial gas bearing being present for radial mounting alongthe shaft and at least two axial gas bearings being present for axialmounting, characterized in that the two axial gas bearings (5, 6) havedifferent surface profiles (12) for generating a flow of the bearing gasin the axial direction (14) of the shaft (2) in order to vent themounting.
 2. The dynamic gas mounting as claimed in claim 1,characterized in that the housing (3) has at least two orifices (8, 9)for the introduction and discharge of the flow of bearing gas.
 3. Thedynamic gas mounting as claimed in claim 2, characterized in that atleast one orifice (8, 9) has a filter element (10) for cleaning theintroduced or discharged flow of bearing gas.
 4. The dynamic gasmounting as claimed in claim 1, characterized in that the two axial gasbearings (5, 6) are designed as spiral-flute axial bearings.
 5. Thedynamic gas mounting as claimed in claim 1, characterized in that theshaft (2) has at least one shaft shoulder (11) for forming the two axialgas bearings (5, 6).
 6. The dynamic gas mounting as claimed in claim 5,characterized in that the shaft shoulder (11) has a first surface (15)with a first surface profile (12) and a second surface (16) with asecond surface profile (12).
 7. The dynamic gas mounting as claimed inclaim 6, characterized in that the first and the second surface profile(12) are formed in annular regions (17) of the first and the secondsurface (15, 16) respectively.
 8. The dynamic gas mounting as claimed inclaim 7, characterized in that the annular regions (17) are arranged ata different distance from the center point (18) of the shaft (2).
 9. Thedynamic gas mounting as claimed in claim 7, characterized in that theannular regions (17) are arranged between an inner radius r_(i) and anouter radius r_(a) of the shaft shoulder (11).
 10. The dynamic gasmounting as claimed in claim 9, characterized in that the annularregions (17) have different outer radii r_(a).
 11. The dynamic gasmounting as claimed in claim 9, characterized in that the annularregions (17) have different inner radii r_(i).
 12. The dynamic gasmounting as claimed in claim 1, characterized in that at least onesurface profile (12) is designed as a stepped profile.
 13. The dynamicgas mounting as claimed in claim 1, characterized in that at least onesurface profile (12) is designed as a partially inward-shaped profile(24).
 14. The dynamic gas mounting as claimed in claim 1, characterizedin that at least one surface profile (12) is designed as a partiallyoutward-shaped profile (25).
 15. The dynamic gas mounting as claimed inclaim 1, characterized in that at least one surface profile (12) isdesigned as a herringbone profile (26).